1. Technical Field
The present invention relates to a signal processing apparatus, a signal processing method, and a computer readable medium storing thereon a program. More particularly, the present invention relates to a signal processing apparatus and a signal processing method for identifying an illumination light component in light received from a subject, and to a computer readable medium storing thereon a program for use with the signal processing apparatus.
2. Related Art
A technique is devised to generate an image signal without an illumination light reflection component by detecting a difference between two visual signals formed by light having two different wavelengths at which an observation target exhibits different light absorption characteristics, as disclosed, for example, in Japanese Patent No. 2643941. Another technique is devised to measure a concentration of a light absorbing substance in a blood without being affected by a change in oxygen saturation, by referring to a light attenuation ratio among a plurality of different wavelengths, as disclosed, for example, in Japanese Patent No. 3972176. Yet another technique is devised to generate a differential image representing a distribution of oxygenated hemoglobin by detecting a difference in two images formed by light of two different wavelengths for which oxygenated hemoglobin exhibits different light reflection characteristics, as disclosed, for example, in Japanese Patent Application Publication No. 2002-272744. Yet another technique is devised to capture a band image of a discrete spectral distribution of a subject by limiting a wavelength range of illumination light used to irradiate the subject, as disclosed, for example, in Japanese Patent Application Publication No. 2002-95635.
These techniques, however, are incapable of producing an image without influence of a pigment of a subject. An image of a living organism cannot be used to accurately judge a condition of an uneven shape such as a lesion of the surface of the living organism before influence of hemoglobin, which is a pigment of the living organism, is eliminated.